1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium that allows for forming a color-developed image and erasing the formed image by controlling thermal energy with the use of a reversible thermosensitive color-developing composition utilizing color-developing reactions between an electron-donating color-forming compound and an electron-accepting compound, relates also a reversible thermosensitive recording label, a member, and an image processing method.
2. Description of the Related Art
Thermosensitive recording compounds utilizing color-developing reactions between electron-donating color-forming compounds (hereinafter otherwise referred to as “color formers” or “leuco dyes”) and electron-accepting compounds (hereinafter otherwise referred to as “developers”) are widely known, and they are widely used as output paper for facsimiles, word processors, scientific measurement devices, etc. along with the development of office automation and also as magnetic thermosensitive cards such as prepaid cards and discount cards. In particular, developments on reversible thermosensitive recording media that allow information and or images to be rewritten any number of times are desired in view of ecological problems and recycling. In Japanese Patent (JP-B) No. 2,981,558, the present inventors proposed a reversible thermosensitive color-developing composition in which an organic phosphoric acid compound having a long-chain aliphatic hydrocarbon group, and an aliphatic carboxylic acid compound or a phenol compound is used as a developer, and a leuco dye serving as a color former is combined therewith; and a reversible thermosensitive recording material using the reversible thermosensitive color-developing composition as a recording layer. This reversible thermosensitive recording material makes it possible to carry out color development and color erasure easily based upon adjustment of heating conditions, sustain the color-developed state and the colorless state stably at normal temperature and repeat color development and color erasure:
As the number of repeatedly rewriting times is increased, the frequency causing reductions in color-developed density is increased due to sedimentation of foreign matters adhering to heat sources such as thermal heads, and ceramic heaters. Further, the amount of energy applied to such heat sources is increased as the conveyance speed of printer is increased, and thus the adhesion amount of foreign matters tends to increase. This causes print defects (a reduction of color-developed density, faded images, ink voids, etc.) and poses a substantial impediment to innovation activities of obtaining high-speed performance of printers.
In order to solve the problem caused at the time of repetitive printing, various examinations have been made so far. For instance, as a method of preventing foreign matters from adhering to thermal head(s), Japanese Patent Application Laid-Open (JP-A) Nos. 2000-25336 and 11-240251 respectively propose a method of providing a protective layer composed of an electron beam curable resin and a filler. This method poses a barrier against thermal propagation from a thermal head to a reversible thermosensitive recording layer, and a reduction in color-developing/color erasure sensitivity is caused, and thus this method cannot be said as efficient. In particular, when the conveyance speed of printer is increased high, the above-mentioned problem is further encouraged. As other methods, Japanese Patent Application Laid-Open (JP-A) No. 2005-53124 proposes a method of utilizing a silicon resin in a protective layer; Japanese Patent Application Laid-Open (JP-A) No. 2002-166649 proposes a method of setting the surface roughness of a protective layer to a specific condition; and Japanese Patent Application Laid-Open (JP-A) No. 9-267568 proposes a method of forming a barrier layer containing an organic material. However, these methods have a problem to cause a degradation of color-developing/color erasure sensitivity, and thus they cannot be said as efficient.
Meanwhile, besides the above-mentioned methods, Japanese Patent Application Laid-Open (JP-A) No. 10-230680 and Japanese Patent (JP-B) No. 3734346 respectively propose making a crosslinked resin for recording layer to thereby increase the strength of the recording layer. However, the function of color-developing/color erasure is yet insufficient by the use of only this method. Further, it is unfavorable because a sufficient color-developed density cannot be obtained, which collaterally affects other properties, for example, storage stability.
Further, as methods of preventing the occurrence of print defects by using a member(s) other than recording media, Japanese Patent Application Laid-Open (JP-A) Nos. 8-45038 and 7-164648 respectively propose a method of removing foreign matters adhering on a thermal head by using a cleaning member; and Japanese Patent Application Laid-Open (JP-A) No. 6-199041 proposes a method of applying a liquid onto a thermal head. Although these methods achieve an object for solving the problems, they are based upon a process different from the color-developing/color erasure process for reversible thermosensitive recording media, and have shortcomings that it takes extra effort and the workability becomes poor, and thus it cannot be said that they can fundamentally solve the problem.
Under such circumstances, it is desired to propose a reversible thermosensitive recording material that causes less adhesion of foreign matters, allows for fast conveyance and is excellent in erasure property in a condition being conveyed fast.